The set of global, packet-switched internetworks known as the Internet is in wide use. A significant proportion of the data traffic that flows through the Internet comprises requests and responses for documents or services based on protocols of the World Wide Web. Much of this traffic comprises HTML documents, or responses from services that respond to requests using HTML. A document is identified by sending a Universal Resource Locator (URL) that uniquely identifies the document from a browser to a server in the network. The hostname part of the URL is resolved, using the Domain Name Service (DNS), into an Internet Protocol (IP) address that identifies a computer that stores the document.
Due to the large volume of network traffic represented by such electronic documents and other network resources, several approaches have been attempted to improve performance by increasing the speed with which networked servers deliver resources to clients. In one approach, a proxy server is used to cache Web pages at a location that is geographically or logically near the requesting client, thereby decreasing server response time and reducing the need for expensive wide area network (WAN) resources.
In another approach, a router is configured as a load balancer to selectively route requests to one of a plurality of replicated servers that serve identical content. This results in faster response times because more server processing power is available to deliver a given set of content.
Still another approach involves placing a plurality of replicated servers in different geographic locations, often remotely located with respect to a master or originating content server. A local content server is either chosen by the end user, or provided automatically. One method that may be used for automatic selection of the closest replica is by providing, during DNS resolution, different IP network addresses in response to successive requests for the same host name. Each IP address identifies a replica located in a different geographic location.
The duration of a session carried out by a client varies greatly. Further, many client sessions involve requests for network resources that contain embedded symbolic references to other network resources. For example, a session may involve a client request for a Web page that has numerous embedded URLs that identify other Web pages or services. Embedded URLs are used to retrieve embedded objects within a Web page. An example of an embedded URL HTTP command: <img src “http://av.com/i/ytl.gif” width=6 height=20>. In this HTTP statement, an embedded URL follows the “img” tag. When a Web browser identifies an embedded URL in an HTML page, the browser automatically loads the HTML document, image or service that is identified by the embedded URL. The embedded URLs may comprise HTML image tags and associated URLs, applet tags that identify a codebase, object tags that identify a codebase, data, and class id, embed tags and URLs, etc.
Thus, an embedded URL forces the Web client to resolve the hostname in order to retrieve the embedded context, even if the user does not wish to continue browsing in the site. Embedded URLs with hostnames that are different from the hostname of the page that contains the embedded URLs are used primarily for commercial advertisements. In such sessions, a significant amount of the time incurred in delivering the Web page may involve resolving the IP addresses of the embedded URLs, using DNS. The time involved in carrying out such DNS resolution significantly increases overall session time, and introduces significant message traffic to the network.
Based on the foregoing, there is a need in this field for an improved method or apparatus for delivering or serving network resources.
There is a particular need for a way to improve the efficiency of Web page retrieval and display, by reducing the number of DNS resolution operations that are carried out.
Improving the efficiency of DNS resolution is also desirable for other reasons and in particular contexts. For example, the Microsoft Windows NT® operating system permits a system administrator to define IP addresses of multiple DNS servers as part of the IP stack configuration parameters. This feature is intended to permit definition of a primary DNS server address and one or more backup DNS server addresses that are used when the primary DNS server is unavailable. However, when multiple DNS servers are defined, the NT operating system will send DNS queries to all the DNS servers that are configured for the IP stack, without waiting for a reply or a timeout error from any of the DNS servers. In the typical case in which one main and one backup DNS server are configured, two DNS queries will be sent for every hostname resolution operation. Unfortunately, the hostname cache of each client stores only up to about ten (10) hostnames by default. This storage capacity is commonly overflowed in normal browsing sessions, resulting in resolution of the same hostnames over and over again.
Thus, there is a specific need for a system or method that can increase the speed with which network resources become available at a client, by improving the efficiency of resolution of hostnames.